<?php
/**
 * @package dompdf
 * @link    https://github.com/dompdf/dompdf
 * @license http://www.gnu.org/copyleft/lesser.html GNU Lesser General Public License
 */
namespace Dompdf\Css;

use DOMElement;
use DOMXPath;
use Dompdf\Css\Content\Url;
use Dompdf\Dompdf;
use Dompdf\Exception;
use Dompdf\FontMetrics;
use Dompdf\Frame\FrameTree;
use Dompdf\Helpers;

/**
 * The master stylesheet class
 *
 * The Stylesheet class is responsible for parsing stylesheets and style
 * tags/attributes.  It also acts as a registry of the individual Style
 * objects generated by the current set of loaded CSS files and style
 * elements.
 *
 * @see Style
 * @package dompdf
 */
class Stylesheet
{
    /**
     * The location of the default built-in CSS file.
     */
    const DEFAULT_STYLESHEET = "/lib/res/html.css";

    /**
     * User agent stylesheet origin
     *
     * @var int
     */
    const ORIG_UA = 1;

    /**
     * User normal stylesheet origin
     *
     * @var int
     */
    const ORIG_USER = 2;

    /**
     * Author normal stylesheet origin
     *
     * @var int
     */
    const ORIG_AUTHOR = 3;

    /**
     * RegEx pattern representing a CSS string
     *
     * @var string
     */
    const PATTERN_CSS_STRING = '(?<CSS_STRING>(?<CSS_STRING_QUOTE>[\'"])(?<CSS_STRING_VALUE>.*?)(?<!\\\\)\g{CSS_STRING_QUOTE})';

    /**
     * RegEx pattern representing the CSS url() function
     *
     * @var string
     */
    const PATTERN_CSS_URL_FN = '(?<CSS_URL_FN>url\(\s*(?<CSS_URL_FN_QUOTE>[\'"]?)(?<CSS_URL_FN_VALUE>.*?)(?(CSS_URL_FN_QUOTE)(?<!\\\\)\g{CSS_URL_FN_QUOTE})\s*\))';

    /**
     * RegEx pattern representing the CSS local() function
     *
     * @var string
     */
    const PATTERN_CSS_LOCAL_FN = '(?<CSS_LOCAL_FN>local\(\s*(?<CSS_LOCAL_FN_QUOTE>[\'"]?)(?<CSS_LOCAL_FN_VALUE>.*?)(?(CSS_LOCAL_FN_QUOTE)(?<!\\\\)\g{CSS_LOCAL_FN_QUOTE})\s*\))';

    /**
     * RegEx pattern representing a CSS media query
     *
     * @var string
     */
    const PATTERN_MEDIA_QUERY = '(?<CSS_MEDIA_QUERY>(?:(?:(?:(?<CSS_MEDIA_QUERY_OP>only|not)\s+)?(?<CSS_MEDIA_QUERY_TYPE>all|aural|bitmap|braille|dompdf|embossed|handheld|paged|print|projection|screen|speech|static|tty|tv|visual))|(?:\(\s*(?<CSS_MEDIA_QUERY_FEATURE>(?:(?:(?:min|max)-)?(?:width|height))|orientation|[^:]*?)\s*(?:\:\s*(?<CSS_MEDIA_QUERY_CONDITION>.*?)\s*)?\))))';

    /*
     * The highest possible specificity is 0x01000000 (and that is only for author
     * stylesheets, as it is for inline styles). Origin precedence can be achieved by
     * adding multiples of 0x10000000 to the actual specificity. Important
     * declarations are handled in Style; though technically they should be handled
     * here so that user important declarations can be made to take precedence over
     * user important declarations, this doesn't matter in practice as Dompdf does
     * not support user stylesheets, and user agent stylesheets can not include
     * important declarations.
     */
    private static $_stylesheet_origins = [
        self::ORIG_UA => 0x00000000, // user agent declarations
        self::ORIG_USER => 0x10000000, // user normal declarations
        self::ORIG_AUTHOR => 0x30000000, // author normal declarations
    ];

    /**
     * Non-CSS presentational hints (i.e. HTML 4 attributes) are handled as if added
     * to the beginning of an author stylesheet, i.e. anything in author stylesheets
     * should override them.
     */
    const SPEC_NON_CSS = 0x20000000;

    /**
     * Current dompdf instance
     *
     * @var Dompdf
     */
    private $_dompdf;

    /**
     * Array of currently defined styles
     *
     * @var array<string, Style[]>
     */
    private $_styles;

    /**
     * Array of embedded files (dataURIs) found in the parsed CSS
     *
     * @var array<string>
     */
    private $_blobs;

    /**
     * Base protocol of the document being parsed
     * Used to handle relative urls.
     *
     * @var string
     */
    private $_protocol = "";

    /**
     * Base hostname of the document being parsed
     * Used to handle relative urls.
     *
     * @var string
     */
    private $_base_host = "";

    /**
     * Base path of the document being parsed
     * Used to handle relative urls.
     *
     * @var string
     */
    private $_base_path = "";

    /**
     * The styles defined by @page rules
     *
     * @var array<Style>
     */
    private $_page_styles;

    /**
     * List of loaded files, used to prevent recursion
     *
     * @var array
     */
    private $_loaded_files;

    /**
     * Current stylesheet origin
     *
     * @var int
     */
    private $_current_origin = self::ORIG_UA;

    /**
     * Accepted CSS media types
     * List of types and parsing rules for future extensions:
     * http://www.w3.org/TR/REC-html40/types.html
     *   screen, tty, tv, projection, handheld, print, braille, aural, all
     * The following are non standard extensions for undocumented specific environments.
     *   static, visual, bitmap, paged, dompdf
     * Note, even though the generated pdf file is intended for print output,
     * the desired content might be different (e.g. screen or projection view of html file).
     * Therefore allow specification of content by dompdf setting Options::defaultMediaType.
     * If given, replace media "print" by Options::defaultMediaType.
     * (Previous version $ACCEPTED_MEDIA_TYPES = $ACCEPTED_GENERIC_MEDIA_TYPES + $ACCEPTED_DEFAULT_MEDIA_TYPE)
     */
    static $ACCEPTED_DEFAULT_MEDIA_TYPE = "print";
    static $ACCEPTED_GENERIC_MEDIA_TYPES = ["all", "static", "visual", "bitmap", "paged", "dompdf"];
    static $VALID_MEDIA_TYPES = ["all", "aural", "bitmap", "braille", "dompdf", "embossed", "handheld", "paged", "print", "projection", "screen", "speech", "static", "tty", "tv", "visual"];

    /**
     * @var FontMetrics
     */
    private $fontMetrics;

    /**
     * The class constructor.
     *
     * The base protocol, host & path are initialized to those of
     * the current script.
     */
    function __construct(Dompdf $dompdf)
    {
        $this->_dompdf = $dompdf;
        $this->setFontMetrics($dompdf->getFontMetrics());
        $this->_styles = [];
        $this->_loaded_files = [];
        $script = __FILE__;
        if (isset($_SERVER["SCRIPT_FILENAME"])) {
            $script = $_SERVER["SCRIPT_FILENAME"];
        }
        list($this->_protocol, $this->_base_host, $this->_base_path) = Helpers::explode_url($script);
        $this->_page_styles = ["base" => new Style($this)];
    }

    /**
     * Set the base protocol
     *
     * @param string $protocol
     */
    function set_protocol(string $protocol)
    {
        $this->_protocol = $protocol;
    }

    /**
     * Set the base host
     *
     * @param string $host
     */
    function set_host(string $host)
    {
        $this->_base_host = $host;
    }

    /**
     * Set the base path
     *
     * @param string $path
     */
    function set_base_path(string $path)
    {
        $this->_base_path = $path;
    }

    /**
     * Return the Dompdf object
     *
     * @return Dompdf
     */
    function get_dompdf()
    {
        return $this->_dompdf;
    }

    /**
     * Return the base protocol for this stylesheet
     *
     * @return string
     */
    function get_protocol()
    {
        return $this->_protocol;
    }

    /**
     * Return the base host for this stylesheet
     *
     * @return string
     */
    function get_host()
    {
        return $this->_base_host;
    }

    /**
     * Return the base path for this stylesheet
     *
     * @return string
     */
    function get_base_path()
    {
        return $this->_base_path;
    }

    /**
     * Get all registered styles as an associative array, indexed by selector.
     *
     * @return array<string, Style[]>
     */
    public function get_styles(): array
    {
        return $this->_styles;
    }

    /**
     * Return the array of page styles
     *
     * @return Style[]
     */
    function get_page_styles()
    {
        return $this->_page_styles;
    }

    /**
     * Create a new Style object associated with this stylesheet
     *
     * @return Style
     */
    function create_style(): Style
    {
        return new Style($this, $this->_current_origin);
    }

    /**
     * Add a new Style object to the stylesheet
     *
     * The style's origin is changed to the current origin of the stylesheet.
     *
     * @param string $key the Style's selector
     * @param Style $style the Style to be added
     */
    function add_style(string $key, Style $style): void
    {
        if (!isset($this->_styles[$key])) {
            $this->_styles[$key] = [];
        }

        $style->set_origin($this->_current_origin);
        $this->_styles[$key][] = $style;
    }

    /**
     * load and parse a CSS string
     *
     * @param string $css
     * @param int $origin
     */
    function load_css(&$css, $origin = self::ORIG_AUTHOR)
    {
        if ($origin) {
            $this->_current_origin = $origin;
        }
        $this->_parse_css($css);
    }

    /**
     * load and parse a CSS file
     *
     * @param string $file
     * @param int $origin
     */
    function load_css_file($file, $origin = self::ORIG_AUTHOR)
    {
        if ($origin) {
            $this->_current_origin = $origin;
        }

        // Prevent circular references
        if (isset($this->_loaded_files[$file])) {
            return;
        }

        $this->_loaded_files[$file] = true;

        if (strpos($file, "data:") === 0) {
            $parsed = Helpers::parse_data_uri($file);
            $css = $parsed["data"];
        } else {
            $options = $this->_dompdf->getOptions();

            $parsed_url = Helpers::explode_url($file);
            $protocol = $parsed_url["protocol"];

            if ($file !== $this->getDefaultStylesheet()) {
                $allowed_protocols = $options->getAllowedProtocols();
                if (!array_key_exists($protocol, $allowed_protocols)) {
                    Helpers::record_warnings(E_USER_WARNING, "Permission denied on $file. The communication protocol is not supported.", __FILE__, __LINE__);
                    return;
                }
                foreach ($allowed_protocols[$protocol]["rules"] as $rule) {
                    [$result, $message] = $rule($file);
                    if (!$result) {
                        Helpers::record_warnings(E_USER_WARNING, "Error loading $file: $message", __FILE__, __LINE__);
                        return;
                    }
                }
            }

            [$css, $http_response_header] = Helpers::getFileContent($file, $this->_dompdf->getHttpContext());

            $good_mime_type = true;

            if (isset($http_response_header) && !$this->_dompdf->getQuirksmode()) {
                foreach ($http_response_header as $_header) {
                    if (preg_match("@Content-Type:\s*([\w/]+)@i", $_header, $matches) &&
                        ($matches[1] !== "text/css")
                    ) {
                        $good_mime_type = false;
                    }
                }
            }
            if (!$good_mime_type || $css === null) {
                Helpers::record_warnings(E_USER_WARNING, "Unable to load css file $file", __FILE__, __LINE__);
                return;
            }

            [$this->_protocol, $this->_base_host, $this->_base_path] = $parsed_url;
        }

        $this->_parse_css($css);
    }

    /**
     * @link https://www.w3.org/TR/CSS21/cascade.html#specificity
     *
     * @param string $selector
     * @param int    $origin
     *    - Stylesheet::ORIG_UA: user agent style sheet
     *    - Stylesheet::ORIG_USER: user style sheet
     *    - Stylesheet::ORIG_AUTHOR: author style sheet
     *
     * @return int
     */
    protected function specificity(string $selector, int $origin = self::ORIG_AUTHOR): int
    {
        $a = ($selector === "!attr") ? 1 : 0;

        $b = min(mb_substr_count($selector, "#"), 255);

        $c = min(mb_substr_count($selector, ".") +
            mb_substr_count($selector, "[") +
            mb_substr_count($selector, ":") -
            2 * mb_substr_count($selector, "::"), 255);

        $d = min(mb_substr_count($selector, " ") +
            mb_substr_count($selector, ">") +
            mb_substr_count($selector, "+") +
            mb_substr_count($selector, "~") -
            mb_substr_count($selector, "~=") +
            mb_substr_count($selector, "::"), 255);

        //If a normal element name is at the beginning of the string,
        //a leading whitespace might have been removed on whitespace collapsing and removal
        //therefore there might be one whitespace less as selected element names
        //this can lead to a too small specificity
        //see selectorToXpath

        if (!in_array($selector[0], [" ", ">", ".", "#", "+", "~", ":", "["], true) && $selector !== "*") {
            $d++;
        }

        if ($this->_dompdf->getOptions()->getDebugCss()) {
            /*DEBUGCSS*/
            print "<pre>\n";
            /*DEBUGCSS*/
            printf("specificity(): 0x%08x \"%s\"\n", self::$_stylesheet_origins[$origin] + (($a << 24) | ($b << 16) | ($c << 8) | ($d)), $selector);
            /*DEBUGCSS*/
            print "</pre>";
        }

        return self::$_stylesheet_origins[$origin] + (($a << 24) | ($b << 16) | ($c << 8) | ($d));
    }

    /**
     * Converts a CSS selector to an XPath query.
     *
     * @param string $selector
     * @param bool   $firstPass
     *
     * @return array|null
     */
    protected function selectorToXpath(string $selector, bool $firstPass = false): ?array
    {
        // Collapse white space and strip whitespace around delimiters
        //$search = array("/\\s+/", "/\\s+([.>#+:])\\s+/");
        //$replace = array(" ", "\\1");
        //$selector = preg_replace($search, $replace, trim($selector));

        // Initial query, always expanded to // below (non-absolute)
        $query = "/";

        // Will contain :before and :after
        $pseudo_elements = [];

        // Parse the selector
        //$s = preg_split("/([ :>.#+])/", $selector, -1, PREG_SPLIT_DELIM_CAPTURE);

        $delimiters = [" ", ">", ".", "#", "+", "~", ":", "[", "("];

        // Add an implicit space at the beginning of the selector if there is no
        // delimiter there already.
        if (!in_array($selector[0], $delimiters, true)) {
            $selector = " $selector";
        }

        $name = "*";
        $len = mb_strlen($selector);
        $i = 0;

        while ($i < $len) {

            $s = $selector[$i];
            $i++;

            // Eat characters up to the next delimiter
            $tok = "";
            $in_attr = false;
            $in_func = false;

            while ($i < $len) {
                $c = $selector[$i];
                $c_prev = $selector[$i - 1];

                if (!$in_func && !$in_attr && in_array($c, $delimiters, true) && !($c === $c_prev && $c === ":")) {
                    break;
                }

                if ($c_prev === "[") {
                    $in_attr = true;
                }
                if ($c_prev === "(") {
                    $in_func = true;
                }

                $tok .= $selector[$i++];

                if ($in_attr && $c === "]") {
                    $in_attr = false;
                    break;
                }
                if ($in_func && $c === ")") {
                    $in_func = false;
                    break;
                }
            }

            switch ($s) {

                case " ":
                case ">":
                    // All elements matching the next token that are descendants
                    // or children of the current token
                    // https://www.w3.org/TR/selectors-3/#descendant-combinators
                    // https://www.w3.org/TR/selectors-3/#child-combinators
                    $expr = $s === " " ? "descendant" : "child";

                    // Tag names are case-insensitive
                    $name = $tok === "" ? "*" : strtolower($tok);
                    $query .= "/$expr::$name";
                    break;

                case "+":
                    // Next-sibling combinator
                    // https://www.w3.org/TR/selectors-3/#sibling-combinators

                    // Tag names are case-insensitive
                    $name = $tok === "" ? "*" : strtolower($tok);
                    $query .= "/following-sibling::*[1]";

                    if ($name !== "*") {
                        $query .= "[name() = '$name']";
                    }
                    break;

                case "~":
                    // Subsequent-sibling combinator
                    // https://www.w3.org/TR/selectors-3/#sibling-combinators

                    // Tag names are case-insensitive
                    $name = $tok === "" ? "*" : strtolower($tok);
                    $query .= "/following-sibling::$name";
                    break;

                case "#":
                    // All elements matching the current token with id equal
                    // to the _next_ token
                    // https://www.w3.org/TR/selectors-3/#id-selectors
                    if ($query === "/") {
                        $query .= "/*";
                    }

                    $query .= "[@id=\"$tok\"]";
                    break;

                case ".":
                    // All elements matching the current token with a class
                    // equal to the _next_ token
                    // https://www.w3.org/TR/selectors-3/#class-html
                    if ($query === "/") {
                        $query .= "/*";
                    }

                    // Match multiple classes: $tok contains the current selected
                    // class.  Search for class attributes with class="$tok",
                    // class=".* $tok .*" and class=".* $tok"

                    // This doesn't work because libxml only supports XPath 1.0...
                    //$query .= "[matches(@$attr,\"^{$tok}\$|^{$tok}[ ]+|[ ]+{$tok}\$|[ ]+{$tok}[ ]+\")]";

                    $query .= "[contains(concat(' ', normalize-space(@class), ' '), concat(' ', '$tok', ' '))]";
                    break;

                case ":":
                    if ($query === "/") {
                        $query .= "/*";
                    }

                    $last = false;

                    // Pseudo-classes
                    switch ($tok) {

                        case "root":
                            $query .= "[not(parent::*)]";
                            break;

                        case "first-child":
                            $query .= "[not(preceding-sibling::*)]";
                            break;

                        case "last-child":
                            $query .= "[not(following-sibling::*)]";
                            break;

                        case "only-child":
                            $query .= "[not(preceding-sibling::*) and not(following-sibling::*)]";
                            break;

                        // https://www.w3.org/TR/selectors-3/#nth-child-pseudo
                        /** @noinspection PhpMissingBreakStatementInspection */
                        case "nth-last-child":
                            $last = true;
                        case "nth-child":
                            $p = $i + 1;
                            $nth = trim(mb_substr($selector, $p, strpos($selector, ")", $i) - $p));
                            $position = $last
                                ? "(count(following-sibling::*) + 1)"
                                : "(count(preceding-sibling::*) + 1)";

                            $condition = $this->selectorAnPlusB($nth, $position);
                            $query .= "[$condition]";
                            break;

                        // TODO: `*:first-of-type`, `*:nth-of-type` etc.
                        // (without fixed element name) are treated equivalent
                        // to their `:*-child` counterparts here. They might
                        // not be properly expressible in XPath 1.0
                        case "first-of-type":
                            $query .= "[not(preceding-sibling::$name)]";
                            break;

                        case "last-of-type":
                            $query .= "[not(following-sibling::$name)]";
                            break;

                        case "only-of-type":
                            $query .= "[not(preceding-sibling::$name) and not(following-sibling::$name)]";
                            break;

                        // https://www.w3.org/TR/selectors-3/#nth-of-type-pseudo
                        /** @noinspection PhpMissingBreakStatementInspection */
                        case "nth-last-of-type":
                            $last = true;
                        case "nth-of-type":
                            $p = $i + 1;
                            $nth = trim(mb_substr($selector, $p, strpos($selector, ")", $i) - $p));
                            $position = $last
                                ? "(count(following-sibling::$name) + 1)"
                                : "(count(preceding-sibling::$name) + 1)";

                            $condition = $this->selectorAnPlusB($nth, $position);
                            $query .= "[$condition]";
                            break;

                        // https://www.w3.org/TR/selectors-4/#empty-pseudo
                        case "empty":
                            $query .= "[not(*) and not(normalize-space())]";
                            break;

                        // TODO: bit of a hack attempt at matches support, currently only matches against elements
                        case "matches":
                            $p = $i + 1;
                            $matchList = trim(mb_substr($selector, $p, strpos($selector, ")", $i) - $p));

                            // Tag names are case-insensitive
                            $elements = array_map("trim", explode(",", strtolower($matchList)));
                            foreach ($elements as &$element) {
                                $element = "name() = '$element'";
                            }

                            $query .= "[" . implode(" or ", $elements) . "]";
                            break;

                        // https://www.w3.org/TR/selectors-3/#UIstates
                        case "disabled":
                        case "checked":
                            $query .= "[@$tok]";
                            break;

                        case "enabled":
                            $query .= "[not(@disabled)]";
                            break;

                        // https://www.w3.org/TR/selectors-3/#dynamic-pseudos
                        // https://www.w3.org/TR/selectors-4/#the-any-link-pseudo
                        case "link":
                        case "any-link":
                            $query .= "[@href]";
                            break;

                        // N/A
                        case "visited":
                        case "hover":
                        case "active":
                        case "focus":
                        case "focus-visible":
                        case "focus-within":
                            $query .= "[false()]";
                            break;

                        // https://www.w3.org/TR/selectors-3/#first-line
                        // https://www.w3.org/TR/selectors-3/#first-letter
                        case "first-line":
                        case ":first-line":
                        case "first-letter":
                        case ":first-letter":
                            // TODO
                            $el = ltrim($tok, ":");
                            $pseudo_elements[$el] = true;
                            break;

                        // https://www.w3.org/TR/selectors-3/#gen-content
                        case "before":
                        case ":before":
                        case "after":
                        case ":after":
                            $pos = ltrim($tok, ":");
                            $pseudo_elements[$pos] = true;
                            if (!$firstPass) {
                                $query .= "/*[@$pos]";
                            }
                            break;

                        // Invalid or unsupported pseudo-class or pseudo-element
                        default:
                            return null;
                    }

                    break;

                case "[":
                    // Attribute selectors.  All with an attribute matching the
                    // following token(s)
                    // https://www.w3.org/TR/selectors-3/#attribute-selectors
                    if ($query === "/") {
                        $query .= "/*";
                    }

                    $attr_delimiters = ["=", "]", "~", "|", "$", "^", "*"];
                    $tok_len = mb_strlen($tok);
                    $j = 0;

                    $attr = "";
                    $op = "";
                    $value = "";

                    while ($j < $tok_len) {
                        if (in_array($tok[$j], $attr_delimiters, true)) {
                            break;
                        }
                        $attr .= $tok[$j++];
                    }

                    if ($attr === "") {
                        // Selector invalid: Missing attribute name
                        return null;
                    }

                    if (!isset($tok[$j])) {
                        // Selector invalid: Missing ] or operator
                        return null;
                    }

                    switch ($tok[$j]) {

                        case "~":
                        case "|":
                        case "^":
                        case "$":
                        case "*":
                            $op .= $tok[$j++];

                            if (!isset($tok[$j]) || $tok[$j] !== "=") {
                                // Selector invalid: Incomplete attribute operator
                                return null;
                            }

                            $op .= $tok[$j];
                            break;

                        case "=":
                            $op = "=";
                            break;

                    }

                    // Read the attribute value, if required
                    if ($op !== "") {
                        $j++;
                        while ($j < $tok_len) {
                            if ($tok[$j] === "]") {
                                break;
                            }
                            $value .= $tok[$j++];
                        }
                    }

                    if (!isset($tok[$j])) {
                        // Selector invalid: Missing ]
                        return null;
                    }

                    $value = trim($value, "\"'");

                    switch ($op) {

                        case "":
                            $query .= "[@$attr]";
                            break;

                        case "=":
                            $query .= "[@$attr=\"$value\"]";
                            break;

                        case "~=":
                            // FIXME: this will break if $value contains quoted strings
                            // (e.g. [type~="a b c" "d e f"])
                            $query .= $value !== "" && !preg_match("/\s+/", $value)
                                ? "[contains(concat(' ', normalize-space(@$attr), ' '), concat(' ', \"$value\", ' '))]"
                                : "[false()]";
                            break;

                        case "|=":
                            $values = explode("-", $value);
                            $query .= "[";

                            foreach ($values as $val) {
                                $query .= "starts-with(@$attr, \"$val\") or ";
                            }

                            $query = rtrim($query, " or ") . "]";
                            break;

                        case "^=":
                            $query .= $value !== ""
                                ? "[starts-with(@$attr,\"$value\")]"
                                : "[false()]";
                            break;

                        case "$=":
                            $query .= $value !== ""
                                ? "[substring(@$attr, string-length(@$attr)-" . (strlen($value) - 1) . ")=\"$value\"]"
                                : "[false()]";
                            break;

                        case "*=":
                            $query .= $value !== ""
                                ? "[contains(@$attr,\"$value\")]"
                                : "[false()]";
                            break;
                    }

                    break;
            }
        }

        return ["query" => $query, "pseudo_elements" => $pseudo_elements];
    }

    /**
     * Parse an `nth-child` expression of the form `an+b`, `odd`, or `even`.
     *
     * @param string $expr
     * @param string $position
     *
     * @return string
     *
     * @link https://www.w3.org/TR/selectors-3/#nth-child-pseudo
     */
    protected function selectorAnPlusB(string $expr, string $position): string
    {
        // odd
        if ($expr === "odd") {
            return "($position mod 2) = 1";
        } // even
        elseif ($expr === "even") {
            return "($position mod 2) = 0";
        } // b
        elseif (preg_match("/^\d+$/", $expr)) {
            return "$position = $expr";
        }

        // an+b
        // https://github.com/tenderlove/nokogiri/blob/master/lib/nokogiri/css/xpath_visitor.rb
        $expr = preg_replace("/\s/", "", $expr);
        if (!preg_match("/^(?P<a>-?[0-9]*)?n(?P<b>[-+]?[0-9]+)?$/", $expr, $matches)) {
            return "false()";
        }

        $a = (isset($matches["a"]) && $matches["a"] !== "") ? ($matches["a"] !== "-" ? intval($matches["a"]) : -1) : 1;
        $b = (isset($matches["b"]) && $matches["b"] !== "") ? intval($matches["b"]) : 0;

        if ($b === 0) {
            return "($position mod $a) = 0";
        } else {
            $compare = ($a < 0) ? "<=" : ">=";
            $b2 = -$b;
            if ($b2 >= 0) {
                $b2 = "+$b2";
            }
            return "($position $compare $b) and ((($position $b2) mod " . abs($a) . ") = 0)";
        }
    }

    /**
     * applies all current styles to a particular document tree
     *
     * apply_styles() applies all currently loaded styles to the provided
     * {@link FrameTree}.  Aside from parsing CSS, this is the main purpose
     * of this class.
     *
     * @param FrameTree $tree
     */
    function apply_styles(FrameTree $tree)
    {
        // Use XPath to select nodes.  This would be easier if we could attach
        // Frame objects directly to DOMNodes using the setUserData() method, but
        // we can't do that just yet.  Instead, we set a _node attribute_ in
        // Frame->set_id() and use that as a handle on the Frame object via
        // FrameTree::$_registry.

        // We create a scratch array of styles indexed by frame id.  Once all
        // styles have been assigned, we order the cached styles by specificity
        // and create a final style object to assign to the frame.

        // FIXME: this is not particularly robust...

        $styles = [];
        $xp = new DOMXPath($tree->get_dom());
        $DEBUGCSS = $this->_dompdf->getOptions()->getDebugCss();

        // Add generated content
        foreach ($this->_styles as $selector => $selector_styles) {
            if (strpos($selector, ":before") === false && strpos($selector, ":after") === false) {
                continue;
            }

            $query = $this->selectorToXpath($selector, true);
            if ($query === null) {
                Helpers::record_warnings(E_USER_WARNING, "The CSS selector '$selector' is not valid", __FILE__, __LINE__);
                continue;
            }

            // Retrieve the nodes, limit to body for generated content
            // TODO: If we use a context node can we remove the leading dot?
            $nodes = @$xp->query('.' . $query["query"]);
            if ($nodes === false) {
                Helpers::record_warnings(E_USER_WARNING, "The CSS selector '$selector' is not valid", __FILE__, __LINE__);
                continue;
            }

            foreach ($selector_styles as $style) {
                foreach ($nodes as $node) {
                    // Only DOMElements get styles
                    if (!($node instanceof DOMElement)) {
                        continue;
                    }

                    foreach (array_keys($query["pseudo_elements"], true, true) as $pos) {
                        // Do not add a new pseudo element if another one already matched
                        if ($node->hasAttribute("dompdf_{$pos}_frame_id")) {
                            continue;
                        }

                        $content = $style->content;

                        // Do not create non-displayed before/after pseudo
                        // elements. Since styles have not been inherited yet,
                        // a specified value of `inherit` will always be treated
                        // as `normal` here. This is fine according to the
                        // CSS 2.1 spec, as any value computes to `normal` on
                        // regular elements
                        // https://www.w3.org/TR/CSS21/generate.html#content
                        // https://www.w3.org/TR/CSS21/generate.html#undisplayed-counters
                        if ($content === "normal" || $content === "none") {
                            continue;
                        }

                        // https://www.w3.org/TR/css-content-3/#content-property
                        $single = count($content) === 1 ? $content[0] : null;

                        if ($single instanceof Url) {
                            $src = $this->resolve_url("url($single->url)", true);
                            $new_node = $node->ownerDocument->createElement("img_generated");
                            $new_node->setAttribute("src", $src);
                        } else {
                            $new_node = $node->ownerDocument->createElement("dompdf_generated");
                        }

                        $new_node->setAttribute($pos, $pos);
                        $new_frame_id = $tree->insert_node($node, $new_node, $pos);
                        $node->setAttribute("dompdf_{$pos}_frame_id", $new_frame_id);
                    }
                }
            }
        }

        // Apply all styles in stylesheet
        foreach ($this->_styles as $selector => $selector_styles) {
            $query = $this->selectorToXpath($selector);
            if ($query === null) {
                Helpers::record_warnings(E_USER_WARNING, "The CSS selector '$selector' is not valid", __FILE__, __LINE__);
                continue;
            }

            // Retrieve the nodes
            $nodes = @$xp->query($query["query"]);
            if ($nodes === false) {
                Helpers::record_warnings(E_USER_WARNING, "The CSS selector '$selector' is not valid", __FILE__, __LINE__);
                continue;
            }

            foreach ($selector_styles as $style) {
                $spec = $this->specificity($selector, $style->get_origin());

                foreach ($nodes as $node) {
                    // Only DOMElements get styles
                    if (!($node instanceof DOMElement)) {
                        continue;
                    }

                    $id = $node->getAttribute("frame_id");

                    // Assign the current style to the scratch array
                    $styles[$id][$spec][] = $style;
                }
            }
        }

        // Set the page width, height, and orientation based on the canvas paper size
        $canvas = $this->_dompdf->getCanvas();
        $paper_width = $canvas->get_width();
        $paper_height = $canvas->get_height();
        $paper_orientation = ($paper_width > $paper_height ? "landscape" : "portrait");

        if ($this->_page_styles["base"] && is_array($this->_page_styles["base"]->size)) {
            $paper_width = $this->_page_styles['base']->size[0];
            $paper_height = $this->_page_styles['base']->size[1];
            $paper_orientation = ($paper_width > $paper_height ? "landscape" : "portrait");
        }

        // Now create the styles and assign them to the appropriate frames. (We
        // iterate over the tree using an implicit FrameTree iterator.)
        $root_flg = false;
        foreach ($tree as $frame) {
            // Helpers::pre_r($frame->get_node()->nodeName . ":");
            if (!$root_flg && $this->_page_styles["base"]) {
                $style = $this->_page_styles["base"];
            } else {
                $style = $this->create_style();
            }

            // Find nearest DOMElement parent
            $p = $frame;
            while ($p = $p->get_parent()) {
                if ($p->get_node()->nodeType === XML_ELEMENT_NODE) {
                    break;
                }
            }

            // Styles can only be applied directly to DOMElements; anonymous
            // frames inherit from their parent
            if ($frame->get_node()->nodeType !== XML_ELEMENT_NODE) {
                $style->inherit($p ? $p->get_style() : null);
                $frame->set_style($style);
                continue;
            }

            $id = $frame->get_id();

            // Handle HTML 4.0 attributes
            AttributeTranslator::translate_attributes($frame);
            if (($str = $frame->get_node()->getAttribute(AttributeTranslator::$_style_attr)) !== "") {
                $styles[$id][self::SPEC_NON_CSS][] = $this->_parse_properties($str);
            }

            // Locate any additional style attributes
            if (($str = $frame->get_node()->getAttribute("style")) !== "") {
                // Destroy CSS comments
                $str = preg_replace("'/\*.*?\*/'si", "", $str);

                $spec = $this->specificity("!attr", self::ORIG_AUTHOR);
                $styles[$id][$spec][] = $this->_parse_properties($str);
            }

            // Grab the applicable styles
            if (isset($styles[$id])) {

                /** @var array[][] $applied_styles */
                $applied_styles = $styles[$id];

                // Sort by specificity
                ksort($applied_styles);

                if ($DEBUGCSS) {
                    $debug_nodename = $frame->get_node()->nodeName;
                    print "<pre>\n$debug_nodename [\n";
                    foreach ($applied_styles as $spec => $arr) {
                        printf("  specificity 0x%08x\n", $spec);
                        /** @var Style $s */
                        foreach ($arr as $s) {
                            print "  [\n";
                            $s->debug_print();
                            print "  ]\n";
                        }
                    }
                }

                // Merge the new styles with the inherited styles
                $acceptedmedia = self::$ACCEPTED_GENERIC_MEDIA_TYPES;
                $acceptedmedia[] = $this->_dompdf->getOptions()->getDefaultMediaType();

                foreach ($applied_styles as $arr) {
                    /** @var Style $s */
                    foreach ($arr as $s) {
                        $media_queries = $s->get_media_queries();
                        if (count($media_queries) > 0) {
                            $media_query_match = false;
                            foreach ($media_queries as $media_query_group) {
                                foreach ($media_query_group as $media_query) {
                                    list($media_query_feature, $media_query_value, $media_query_operator) = $media_query;
                                    switch ($media_query_feature) {
                                        case "height":
                                            $feature_match = $paper_height === (float)$style->length_in_pt($media_query_value);
                                            break;
                                        case "min-height":
                                            $feature_match = $paper_height >= (float)$style->length_in_pt($media_query_value);
                                            break;
                                        case "max-height":
                                            $feature_match = $paper_height <= (float)$style->length_in_pt($media_query_value);
                                            break;
                                        case "width":
                                            $feature_match = $paper_width === (float)$style->length_in_pt($media_query_value);
                                            break;
                                        case "min-width":
                                            $feature_match = $paper_width >= (float)$style->length_in_pt($media_query_value);
                                            break;
                                        case "max-width":
                                            $feature_match = $paper_width <= (float)$style->length_in_pt($media_query_value);
                                            break;
                                        case "orientation":
                                            $feature_match = $paper_orientation === $media_query_value;
                                            break;
                                        case "type":
                                            $feature_match = in_array($media_query_value, $acceptedmedia, true);
                                            break;
                                        default:
                                            Helpers::record_warnings(E_USER_WARNING, "Unknown media query: $media_query_feature", __FILE__, __LINE__);
                                            continue (2); // unknown query, move to the next grouping
                                    }
                                    $negate = $media_query_operator === "not";
                                    if ($negate xor !$feature_match) {
                                        continue (2); // failed query match, move to the next grouping
                                    }
                                }
                                $media_query_match = true;
                            }
                            if (!$media_query_match) {
                                continue;
                            }
                        }
                        $style->merge($s);
                    }
                }
            }

            // Handle inheritance
            if ($p && $DEBUGCSS) {
                print "  inherit [\n";
                $p->get_style()->debug_print();
                print "  ]\n";
            }

            $style->inherit($p ? $p->get_style() : null);

            if ($DEBUGCSS) {
                print "  DomElementStyle [\n";
                $style->debug_print();
                print "  ]\n";
                print "]\n</pre>";
            }

            $style->clear_important();
            $frame->set_style($style);

            if (!$root_flg && $this->_page_styles["base"]) {
                $root_flg = true;

                // set the page width, height, and orientation based on the parsed page style
                if ($style->size !== "auto") {
                    list($paper_width, $paper_height) = $style->size;
                }
                $paper_width = $paper_width - (float)$style->length_in_pt($style->margin_left) - (float)$style->length_in_pt($style->margin_right);
                $paper_height = $paper_height - (float)$style->length_in_pt($style->margin_top) - (float)$style->length_in_pt($style->margin_bottom);
                $paper_orientation = ($paper_width > $paper_height ? "landscape" : "portrait");
            }
        }

        // We're done!  Clean out the registry of all styles since we
        // won't be needing this later.
        foreach (array_keys($this->_styles) as $key) {
            $this->_styles[$key] = null;
            unset($this->_styles[$key]);
        }
    }

    /**
     * parse a CSS string using a regex parser
     * Called by {@link Stylesheet::parse_css()}
     *
     * @param string $str
     */
    private function _parse_css($str)
    {
        $str = trim($str);

        // Destroy comments and remove HTML comments
        $css = preg_replace([
            "'/\*.*?\*/'si",
            "/^<!--/",
            "/-->$/"
        ], "", $str);

        // shim constants for string interpolation
        $pattern_atimport_string = str_replace("CSS_STRING", "CSS_ATIMPORT_STRING", self::PATTERN_CSS_STRING);
        $pattern_atimport_url = str_replace("CSS_URL_FN", "CSS_ATIMPORT_URL_FN", self::PATTERN_CSS_URL_FN);
        $pattern_media_query = self::PATTERN_MEDIA_QUERY;

        // Something more legible:
        // ... does not handle '{' within strings, e.g. [attr="string {}"]
        $re = <<<EOL
            /
                # Skip leading whitespace
                \s*
                
                # Match at-rules
                (?<CSS_ATRULE>@(?<CSS_ATRULE_IDENTIFIER>
                    (?<CSS_ATFONT>font-face)
                    |(?<CSS_ATIMPORT>import)
                    |(?<CSS_ATMEDIA>media)
                    |(?<CSS_ATPAGE>page)
                    |(?<CSS_AT>[\w-]*)
                ))?
                
                # Branch to process segment following at-rule match
                (?(CSS_ATRULE)(?:
                    (?(CSS_ATFONT)\s*{(?<CSS_ATFONT_BODY>.*?)})
                    (?(CSS_ATIMPORT)\s*(?<CSS_ATIMPORT_RULE>
                        (?<CSS_ATIMPORT_URL>
                            {$pattern_atimport_string}
                            |{$pattern_atimport_url}
                        )
                        (?<CSS_ATIMPORT_MEDIA_QUERY>.*?)
                    );)
                    (?(CSS_ATMEDIA)\s*(?<CSS_ATMEDIA_RULE>[^{]*){(?<CSS_ATMEDIA_BODY> (?:(?>[^{}]+) (?<CSS_ATMEDIA_BODY_BRACKET>{)?
                        (?(CSS_ATMEDIA_BODY_BRACKET) (?>[^}]*) }) \s*)+?
                    )})
                    (?(CSS_ATPAGE)\s*(?<CSS_ATPAGE_RULE>[^{]*){(?<CSS_ATPAGE_BODY>.*?)})
                    (?(CSS_AT)\s*([^{;]*)(;|{(?<CSS_AT_BODY> (?:(?>[^{}]+) (?<CSS_AT_BODY_BRACKET>{)?
                        (?(CSS_AT_BODY_BRACKET) (?>[^}]*) }) \s*)+?
                    )}))
                )
                
                # Branch to match regular rules (not preceded by '@')
                |(?<CSS_RULESET>[^{]*{[^}]*}))
            /isx
EOL;

        // replace data URIs with blob URIs
        while (($start = strpos($css, "data:")) !== false) {
            $len = null;
            if (preg_match("/['\"\)]/", $css, $matches, PREG_OFFSET_CAPTURE, $start)) {
                $len = $matches[0][1] - $start;
            }
            $data_uri = substr($css, $start, $len);
            $data_uri_hash = md5($data_uri);
            $this->_blobs[$data_uri_hash] = $data_uri;
            $css = substr($css, 0, $start) . "blob://" . $data_uri_hash . ($len > 0 ? substr($css, $start + $len) : "");
        }

        $matches = [];
        if (preg_match_all($re, $css, $matches, PREG_SET_ORDER) === false || count($matches) === 0) {
            global $_dompdf_warnings;
            $_dompdf_warnings[] = "Unable to parse CSS that starts with: " . substr($str, 0, 100);
            return;
        }

        $media_query_regex = "/{$pattern_media_query}/isx";
        $accepted_media = self::$ACCEPTED_GENERIC_MEDIA_TYPES;
        $accepted_media[] = $this->_dompdf->getOptions()->getDefaultMediaType();
        foreach ($matches as $match) {
            if ($match["CSS_ATRULE_IDENTIFIER"] !== "") {
                $atrule_identifier = strtolower($match["CSS_ATRULE_IDENTIFIER"]);
                // Handle @rules
                switch ($atrule_identifier) {

                    case "import":
                        $this->_parse_import($match["CSS_ATIMPORT_URL"], $match["CSS_ATIMPORT_MEDIA_QUERY"]);
                        break;

                    case "media":
                        $mq = [];
                        $media_queries = preg_split("/\s*(,|\Wor\W)\s*/", mb_strtolower(trim($match["CSS_ATMEDIA_RULE"])));
                        foreach ($media_queries as $media_query) {
                            $media_query_matches = [];
                            if (preg_match_all($media_query_regex, $media_query, $media_query_matches, PREG_SET_ORDER) === false) {
                                continue;
                            }

                            $mq_grouping = [];
                            foreach ($media_query_matches as $media_query_match) {
                                if (empty($media_query_match["CSS_MEDIA_QUERY_TYPE"]) === false) {
                                    $media_query_feature = "type";
                                    $media_query_value = strtolower($media_query_match["CSS_MEDIA_QUERY_TYPE"]);
                                    $media_query_operator = strtolower($media_query_match["CSS_MEDIA_QUERY_OP"]);
                                } elseif (empty($media_query_match["CSS_MEDIA_QUERY_FEATURE"]) === false) {
                                    $media_query_feature = strtolower($media_query_match["CSS_MEDIA_QUERY_FEATURE"]);
                                    $media_query_value = (array_key_exists("CSS_MEDIA_QUERY_CONDITION", $media_query_match) ? strtolower($media_query_match["CSS_MEDIA_QUERY_CONDITION"]) : null);
                                    $media_query_operator = strtolower($media_query_match["CSS_MEDIA_QUERY_OP"]);
                                } else {
                                    // partial error handling implementation per https://www.w3.org/TR/css3-mediaqueries/#error-handling
                                    $media_query_feature = "type";
                                    $media_query_value = "all";
                                    $media_query_operator = "not";
                                }
                                $mq_grouping[] = [$media_query_feature, $media_query_value, $media_query_operator];
                            }
                            if (count($mq_grouping) > 0) {
                                $mq[] = $mq_grouping;
                            }
                        }
                        $this->_parse_sections($match["CSS_ATMEDIA_BODY"], $mq);
                        break;

                    case "page":
                        //This handles @page to be applied to page oriented media
                        //Note: This has a reduced syntax:
                        //@page { margin:1cm; color:blue; }
                        //Not a sequence of styles like a full.css, but only the properties
                        //of a single style, which is applied to the very first "root" frame before
                        //processing other styles of the frame.
                        //Working properties:
                        // margin (for margin around edge of paper)
                        // font-family (default font of pages)
                        // color (default text color of pages)
                        //Non working properties:
                        // border
                        // padding
                        // background-color
                        //Todo:Reason is unknown
                        //Other properties (like further font or border attributes) not tested.
                        //If a border or background color around each paper sheet is desired,
                        //assign it to the <body> tag, possibly only for the css of the correct media type.

                        // If the page has a name, skip the style.
                        $page_selector = trim($match["CSS_ATPAGE_RULE"]);

                        $key = null;
                        switch ($page_selector) {
                            case "":
                                $key = "base";
                                break;

                            case ":left":
                            case ":right":
                            case ":odd":
                            case ":even":
                            /** @noinspection PhpMissingBreakStatementInspection */
                            case ":first":
                                $key = $page_selector;
                                break;

                            default:
                                break 2;
                        }

                        // Store the style for later...
                        if (empty($this->_page_styles[$key])) {
                            $this->_page_styles[$key] = $this->_parse_properties($match["CSS_ATPAGE_BODY"]);
                        } else {
                            $this->_page_styles[$key]->merge($this->_parse_properties($match["CSS_ATPAGE_BODY"]));
                        }
                        break;

                    case "font-face":
                        $this->_parse_font_face($match["CSS_ATFONT_BODY"]);
                        break;

                    default:
                        // ignore everything else
                        break;
                }

                continue;
            }

            if ($match["CSS_RULESET"] !== "") {
                $this->_parse_sections($match["CSS_RULESET"]);
            }
        }
    }

    /**
     * Resolve the given `url()` declaration to an absolute URL.
     *
     * @param string|null $val The declaration to resolve in the context of the stylesheet.
     * @param bool|null   $resolve_blobs Indicates whether or not to resolve blob URLs to their final value.
     * @return string     The resolved URL, or `none`, if the value is `none`,
     *                    invalid, or points to a non-existent local file.
     */
    public function resolve_url($val, $resolve_blobs = false): string
    {
        $DEBUGCSS = $this->_dompdf->getOptions()->getDebugCss();

        static $pattern = "/" . self::PATTERN_CSS_URL_FN . "/isx";
        if ($val === null || $val === "" || strcasecmp($val, "none") === 0) {
            $path = "none";
        } elseif (preg_match($pattern, $val, $matches)) {
            // Resolve the url now in the context of the current stylesheet
            $url = $matches["CSS_URL_FN_VALUE"];
            switch ($matches["CSS_URL_FN_QUOTE"]) {
                case "\"":
                    $url = str_replace("\\\"", "\"", $url);
                    break;
                case "'":
                    $url = str_replace("\\'", "'", $url);
                    break;
                default:
                    $url = str_replace(["\\(", "\\)"], ["(", ")"], $url);
                    break;
            }
            if ($resolve_blobs === true && strpos($url, "blob://") !== false) {
                $url = $this->_blobs[substr($url, 7)];
            }
            $path = Helpers::build_url(
                $this->_protocol,
                $this->_base_host,
                $this->_base_path,
                $url
            );
            if ($path === null) {
                $path = "none";
            }
        } else {
            $path = "none";
        }
        if ($DEBUGCSS) {
            $parsed_url = Helpers::explode_url($path);
            print "<pre>[_image\n";
            print_r($parsed_url);
            print $this->_protocol . "\n" . $this->_base_path . "\n" . $path . "\n";
            print "_image]</pre>";
        }
        return $path;
    }

    /**
     * parse @import at-rule
     *
     * @param string $url the url of the imported CSS file
     */
    private function _parse_import($url, $import_media_query)
    {
        // if URL is a CSS string, wrap it in the url function for parsing by the resolve_url method
        if (mb_strpos($url, "url(") === false) {
            $url = "url($url)";
        }
        if (($url = $this->resolve_url($url, true)) === "none") {
            return;
        }

        // Store our current base url properties in case the new url is elsewhere
        $protocol = $this->_protocol;
        $host = $this->_base_host;
        $path = $this->_base_path;

        $media_query_regex = "/" . self::PATTERN_MEDIA_QUERY . "/isx";
        $media_queries = preg_split("/\s*(,|\Wor\W)\s*/", mb_strtolower(trim($import_media_query ?? "")));
        if (count($media_queries) === 0) {
            $this->load_css_file($url, $this->_current_origin);
        } else {
            // Set the page width, height, and orientation based on the canvas paper size
            $canvas = $this->_dompdf->getCanvas();
            $paper_width = $canvas->get_width();
            $paper_height = $canvas->get_height();
            $paper_orientation = ($paper_width > $paper_height ? "landscape" : "portrait");

            $style = $this->_page_styles["base"] ?? new Style($this);
            if (is_array($style->size)) {
                $paper_width = $style->size[0];
                $paper_height = $style->size[1];
                $paper_orientation = ($paper_width > $paper_height ? "landscape" : "portrait");
            }

            $acceptedmedia = self::$ACCEPTED_GENERIC_MEDIA_TYPES;
            $acceptedmedia[] = $this->_dompdf->getOptions()->getDefaultMediaType();

            foreach ($media_queries as $media_query) {
                $media_query_matches = [];
                if (preg_match_all($media_query_regex, $media_query, $media_query_matches, PREG_SET_ORDER) === false) {
                    continue;
                }

                foreach ($media_query_matches as $media_query_match) {
                    if (empty($media_query_match["CSS_MEDIA_QUERY_TYPE"]) === false) {
                        $media_query_feature = "type";
                        $media_query_value = strtolower($media_query_match["CSS_MEDIA_QUERY_TYPE"]);
                        $media_query_operator = strtolower($media_query_match["CSS_MEDIA_QUERY_OP"]);
                    } elseif (empty($media_query_match["CSS_MEDIA_QUERY_FEATURE"]) === false) {
                        $media_query_feature = strtolower($media_query_match["CSS_MEDIA_QUERY_FEATURE"]);
                        $media_query_value = (array_key_exists("CSS_MEDIA_QUERY_CONDITION", $media_query_match) ? strtolower($media_query_match["CSS_MEDIA_QUERY_CONDITION"]) : null);
                        $media_query_operator = strtolower($media_query_match["CSS_MEDIA_QUERY_OP"]);
                    } else {
                        // partial error handling implementation per https://www.w3.org/TR/css3-mediaqueries/#error-handling
                        $media_query_feature = "type";
                        $media_query_value = "all";
                        $media_query_operator = "not";
                    }

                    switch ($media_query_feature) {
                        case "height":
                            $feature_match = $paper_height === (float)$style->length_in_pt($media_query_value);
                            break;
                        case "min-height":
                            $feature_match = $paper_height >= (float)$style->length_in_pt($media_query_value);
                            break;
                        case "max-height":
                            $feature_match = $paper_height <= (float)$style->length_in_pt($media_query_value);
                            break;
                        case "width":
                            $feature_match = $paper_width === (float)$style->length_in_pt($media_query_value);
                            break;
                        case "min-width":
                            $feature_match = $paper_width >= (float)$style->length_in_pt($media_query_value);
                            break;
                        case "max-width":
                            $feature_match = $paper_width <= (float)$style->length_in_pt($media_query_value);
                            break;
                        case "orientation":
                            $feature_match = $paper_orientation === $media_query_value;
                            break;
                        case "type":
                            $feature_match = in_array($media_query_value, $acceptedmedia, true);
                            break;
                        default:
                            Helpers::record_warnings(E_USER_WARNING, "Unknown media query: $media_query_feature", __FILE__, __LINE__);
                            continue (2);
                    }
                    $negate = $media_query_operator === "not";
                    if ($negate xor !$feature_match) {
                        continue (2);
                    }
                }

                //TODO: pass media queries as an argument to load_css_file and apply to all contained styles
                //      to better accommodate styling content in, for example, documents with varying page orientations
                $this->load_css_file($url, $this->_current_origin);
                break; // stop here so we don't load the same CSS more than once (at least until we implement that TODO)
            }
        }

        // Restore the current base url
        $this->_protocol = $protocol;
        $this->_base_host = $host;
        $this->_base_path = $path;
    }

    /**
     * parse @font-face{} sections
     * http://www.w3.org/TR/css3-fonts/#the-font-face-rule
     *
     * @param string $str CSS @font-face rules
     */
    private function _parse_font_face($str)
    {
        $descriptors = $this->_parse_properties($str);

        preg_match_all("/" . self::PATTERN_CSS_LOCAL_FN . "|" . self::PATTERN_CSS_URL_FN . "\s*(?<FORMAT>format\s*\((?<FORMAT_VALUE>collection|embedded-opentype|opentype|svg|truetype|woff|woff2|" . self::PATTERN_CSS_STRING . ")\))?/i", $descriptors->src, $sources, PREG_SET_ORDER);

        $valid_sources = [];
        foreach ($sources as $source) {
            $urlfn = $source["CSS_URL_FN"] ?? "";
            $format = strtolower($source["CSS_STRING_VALUE"] ?? $source["FORMAT_VALUE"] ?? "truetype");

            if ($urlfn !== "" && $format === "truetype") {
                $url = $this->resolve_url($urlfn, true);
                if ($url === "none") {
                    continue;
                }
                $source_info = [
                    "uri" => $urlfn,
                    "format" => $format,
                    "path" => $url,
                ];
                $valid_sources[] = $source_info;
            }
        }

        if (empty($valid_sources)) {
            return;
        }

        $style = [
            "family" => $descriptors->get_font_family_raw(),
            "weight" => $descriptors->font_weight,
            "style" => $descriptors->font_style,
        ];

        foreach ($valid_sources as $valid_source) {
            if ($this->fontMetrics->registerFont($style, $valid_source["path"], $this->_dompdf->getHttpContext())) {
                break;
            }
        }
    }

    /**
     * parse regular CSS blocks
     *
     * _parse_properties() creates a new Style object based on the provided
     * CSS rules.
     *
     * @param string $str CSS rules
     * @return Style
     */
    private function _parse_properties($str)
    {
        $DEBUGCSS = $this->_dompdf->getOptions()->getDebugCss();

        if ($DEBUGCSS) {
            print '[_parse_properties';
        }

        $delims = ['"' => '"', "'" => "'", '(' => ')'];
        $delim = null;
        $len = strlen($str);
        $properties = [];
        $char = null;
        $prev = null;
        for ($pos = 0; $pos < $len; $pos++) {
            $prev = $char;
            $char = $str[$pos];
            if ($delim !== null) {
                if ($char === $delims[$delim] && $prev !== '\\') {
                    $delim = null;
                }
                continue;
            }
            if (isset($delims[$char]) && $prev !== '\\') {
                $delim = $char;
                continue;
            }
            if ($char === ';' && $prev !== '\\') {
                $properties[] = substr($str, 0, $pos);
                $str = substr($str, $pos+1);
                $pos = 0;
                $len = strlen($str);
            }
        }
        $properties[] = $str;
        $style = new Style($this, Stylesheet::ORIG_AUTHOR);
        foreach ($properties as $prop) {
            $prop = str_replace("\\;", ";", trim($prop));
            if ($prop === "") {
                continue;
            }

            $important = false;
            if (substr($prop, -9) === 'important') {
                $prop_tmp = rtrim(substr($prop, 0, -9));

                if (substr($prop_tmp, -1) === '!') {
                    $prop = rtrim(substr($prop_tmp, 0, -1));
                    $important = true;
                }
            }

            $i = strpos($prop, ":");
            if ($i === false) {
                if ($DEBUGCSS) {
                    print "(novalue $prop)";
                }
                continue;
            }

            $prop_name = rtrim(substr($prop, 0, $i));
            $value = ltrim(substr($prop, $i + 1));

            // Regular (non-custom) properties are case-insensitive
            if (strncmp($prop_name, "--", 2) !== 0) {
                $prop_name = strtolower($prop_name);
            }

            if ($DEBUGCSS) {
                print "($prop_name:=$value" . ($important ? " !IMPORTANT" : "") . ")";
            }

            $style->set_prop($prop_name, $value, $important, false);
        }

        if ($DEBUGCSS) {
            print '_parse_properties]';
        }

        return $style;
    }

    /**
     * parse selector + rulesets
     *
     * @param string $str CSS selectors and rulesets
     * @param array $media_queries
     */
    private function _parse_sections($str, $media_queries = [])
    {
        // Pre-process selectors: collapse all whitespace and strip whitespace
        // around '>', '.', ':', '+', '~', '#'
        $patterns = ["/\s+/", "/\s+([>.:+~#])\s+/"];
        $replacements = [" ", "\\1"];
        $DEBUGCSS = $this->_dompdf->getOptions()->getDebugCss();

        $sections = explode("}", $str);
        if ($DEBUGCSS) print '[_parse_sections';
        foreach ($sections as $sect) {
            $i = mb_strpos($sect, "{");
            if ($i === false) { continue; }

            if ($DEBUGCSS) print '[section';

            $selector_str = preg_replace($patterns, $replacements, mb_substr($sect, 0, $i));
            $selectors = preg_split("/,(?![^\(]*\))/", $selector_str, 0, PREG_SPLIT_NO_EMPTY);
            $style = $this->_parse_properties(trim(mb_substr($sect, $i + 1)));

            // Assign it to the selected elements
            foreach ($selectors as $selector) {
                $selector = trim($selector);

                if ($selector === "") {
                    if ($DEBUGCSS) print '#empty#';
                    continue;
                }
                if ($DEBUGCSS) print '#' . $selector . '#';
                //if ($DEBUGCSS) { if (strpos($selector,'p') !== false) print '!!!p!!!#'; }

                //FIXME: tag the selector with a hash of the media query to separate it from non-conditional styles (?), xpath comments are probably not what we want to do here
                if (count($media_queries) > 0) {
                    $style->set_media_queries($media_queries);
                }
                $this->add_style($selector, $style);
            }

            if ($DEBUGCSS) {
                print 'section]';
            }
        }

        if ($DEBUGCSS) {
            print "_parse_sections]\n";
        }
    }

    /**
     * @return string
     */
    public function getDefaultStylesheet()
    {
        $options = $this->_dompdf->getOptions();
        $rootDir = realpath($options->getRootDir());
        return Helpers::build_url("file://", "", $rootDir, $rootDir . self::DEFAULT_STYLESHEET);
    }

    /**
     * @param FontMetrics $fontMetrics
     * @return $this
     */
    public function setFontMetrics(FontMetrics $fontMetrics)
    {
        $this->fontMetrics = $fontMetrics;
        return $this;
    }

    /**
     * @return FontMetrics
     */
    public function getFontMetrics()
    {
        return $this->fontMetrics;
    }

    /**
     * dumps the entire stylesheet as a string
     *
     * Generates a string of each selector and associated style in the
     * Stylesheet.  Useful for debugging.
     *
     * @return string
     */
    function __toString()
    {
        $str = "";
        foreach ($this->_styles as $selector => $selector_styles) {
            foreach ($selector_styles as $style) {
                $str .= "$selector => " . $style->__toString() . "\n";
            }
        }

        return $str;
    }
}
